A polysilane is a high-molecular compound having a silicon-silicon bond as a main chain and is a material having various physical properties (for example, heat resistance, high refractive index, photoreactivity, hole transportability, luminescence, etching resistance, and low dielectric constant). From such excellent physical properties, the polysilane is attracting the attention as a ceramic precursor, an interlayer insulation film, and a photoelectric material (for example, a photo resist, a photoelectrically photographic material such as an organic photoreceptor, an optically transmissive material such as a light guide, an optically recording material such as an optical memory, and an electroluminescent device).
For such an application, the polysilane is practically used or applied in the form of a thin film. To form the thin film, the polysilane is usually required to have solubility in a solvent (an organic solvent), however, the solubility is sometimes insufficient depending on the species of the polysilane. In particular, since a polysilane having a regular structure (e.g., a homopolymer) is soluble in a limited number of solvents, the use of the polysilane is sometimes limited.
Moreover, in order to expand the scope of the use of the polysilane, it is necessary to impart other functions to the polysilane. However, the polysilane restricts a substituent thereof to extremely few species compared to other carbonaceous compounds. Therefore, it is very difficult to impart other functions to the polysilane or control the physical properties of the polysilane. This difficulty is attributable to the following reasons: most of industrially (or commercially) mass-produced chlorosilane compounds commonly used as a raw material for a polysilane are chlorosilane compounds having an alkyl group or a phenyl group as a substituent, and chlorosilane compounds having other structures are expensive or difficult to synthesize in large quantities.
Further, in order to impart the functionality to the polysilane, it is considered that a chlorosilane compound having a functional substituent (for example, a hydroxyl group, a carboxyl group, and an epoxy group) is synthesized to use for production of a polysilane. However, in such a manner, the functional substituent blocks a synthesis reaction of the polysilane or is denatured and loses functions thereof. Accordingly, it is very difficult to impart the functionality to the polysilane through the use of a monomer having a functional substituent.
Then a process for polymerizing a monomer having a functional substituent that is protected by a protective group has been proposed. For example, Japanese Patent Application Laid-Open No. 39358/1993 (JP-5-39358A, Patent Document 1) discloses a process which comprises eliminating a silyl group from a polysilane having a phenol group protected by the silyl group to give a polysilane having a phenolic hydroxyl group. Specifically, in Example 1, a polysilane having a phenolic hydroxyl group is synthesized by allowing m-bromophenol to react with t-butyldimethylsilyl chloride to give m-(t-butyldimethylsilyloxy)bromobenzene, preparing a Grignard reagent from the resulting m-(t-butyldimethylsilyloxy)bromobenzene and metal magnesium, allowing the reagent to react with tetrachlorosilane to give di[m-(t-butyldimethylsilyloxy)phenyl]dichlorosilane, polymerizing the resulting compound to give a polysilane, and eliminating the protective group from the polysilane. However, a chlorosilane compound having a phenolic hydroxyl group does not exist generally, and even if such a compound is synthesized, it is difficult to polymerize the compound by the process of the document. Additionally, the process of the document not only requires a lot of extremely complicated steps (including protecting a hydroxyl group of a phenol compound, Grignard-reacting the protected phenol compound with tetrachlorosilane, forming a polysilane by polymerization, and eliminating the protective group from the phenol group of the polysilane) but also produces a polysilane having a poor functionality.
Moreover, a method utilizing a terminal group of the polysilane has been known as a method for imparting the functionality to a polysilane. For example, Japanese Patent Application Laid-Open No. 192429/1994 (JP-6-192429A, Patent Document 2) discloses a process which comprises adding reactive substituents to both ends of a polysilane. In the process of the document, a polysilane having reactivity in both ends thereof is obtained by allowing a chloropolysilane having chlorine atoms in both ends thereof to react with LiAlH4 for reduction to give a hydroxypolysilane having hydroxyl groups in both ends thereof, and addition-reacting the resulting polysilane with a reactive compound containing an unsaturated group (e.g., allyl glycidyl ether and trimethoxyvinylsilane) in the presence of a hydrosilylation catalyst. However, the process of the document requires a complicated two-step reaction, and additionally, only two reactive substituents can be introduced to one polysilane molecule at the maximum. Therefore, the molecular design (such as an introduction of reactive substituents in a high density or an extensive change in solubility in a solvent) is restricted.
Incidentally, as a process for producing a polysilane, various processes have been known. For example, International Publication WO98/29476 pamphlet (Patent Document 3) discloses a process for producing a polysilane by acting magnesium or a magnesium alloy on a dihalosilane in the presence of a lithium salt and a metal halide in an aprotic solvent.    [Patent Document 1] JP-5-39358A (Claims and Examples)    [Patent Document 2] JP-6-192429A (Claims and Examples)    [Patent Document 3] WO98/29476 (Claims)